Neuronal apoptosis plays an essential role in normal brain development and neurodegeneration. Results of recent studies indicate that after brain injury this type of neuronal death preferentially proceeds through the intrinsic pathway of caspase activation. The release of mitochondrial cytochrome c (Cyto-c) to the cytoplasm plays a central role in this pathway. Cyto-c release is mediated by pro-apoptotic members of Bcl-2 family, which are induced in injured neurons in response to DNA damage. On the other hand, other reports indicate that the release of Cyto-c from mitochondria is not sufficient for the induction of the intrinsic apoptotic pathway. Despite of Cyto-c release, progression of this pathway is inhibited by the extracellular signal-regulated protein kinases Erk1/2 able to block activation of caspase-9 and promote cell survival by direct phosphorylation of procaspase-9. A pathway, which restrains this protective mechanism in apoptotic neurons, remains unknown. In this application we propose a possible link between DNA damage, the release of Cyto-c from mitochondria, dephosphorylation and inactivation of pro-survival Erk1/2, activation of caspases, and neuronal death. Our working hypothesis is that the progression of DNA damage-induced apoptosis in neurons depends on p53-mediated activation of specific dual specificity phosphatases (DUSPs) able to promote processing of procaspase-9 through selective Erk1/2 inactivation. If our hypothesis is correct, inhibition of DUSP activity after neuronal injury must be neuroprotective. To address the hypothesis, we propose 2 related Specific Aims: (1) To examine neuronal expression of DUSP gene family members in response to DNA damage in vitro and after brain trauma in vivo and (2) To assess a role for inducible DUSPs in inhibition of Erk1/2, caspase activation, and neuronal death. Results of this study may have fundamental impact on identifying novel treatment strategies for a wide variety of acute and chronic neurodegenerative conditions where the contribution of DNA damage and p53-dependent apoptosis to neuronal loss is highly significant. [unreadable] [unreadable] [unreadable]